The production of organic products in situ by heating and/or fracturing subsurface formations containing hydrocarbons, such as oil shale or coal beneath overburdens, is desirable but has generally been uneconomical since large amounts of energy are required for fracturing or heating the formation, for example, by injection of heated fluids, by subsurface combustion in the presence of an injected oxidizer, or by nuclear explosion. In the alternative, it has been either necessary to mine the oil shale or coal and convert it to the desired products such as pipe lineable oil or gas or other products on the surface resulting in substantial quantities of residue, particularly in the case of oil shale where the spent oil shale has a larger volume than the original oil shale. In addition, if the kerogen in the oil shale is overheated, the components may not flow or may decompose to undesirable products such as carbonized oil shale which will not flow through fractures formed in the oil shale. In addition, at temperatures above 1000.degree. F., water locked in the shale will be released and the shale can decompose absorbing large amounts of heat and thus wasting input heating energy.